The present invention relates generally to inductive write heads used in magnetic media storage devices, and more particularly to magneto-resistive disk drive heads.
A computer disk drive stores-and retrieves data by positioning a magnetic read/write head over a rotating magnetic data storage disk. The head, or heads, which are typically arranged in stacks, read from or write data to concentric data tracks defined on the surface of the disks which are also typically arranged in stacks. The heads are included in structures called xe2x80x9cslidersxe2x80x9d into which the read/write sensors are imbedded during fabrication. The goal in recent years is to increase the amount of data that can be stored on each hard disk. If data tracks can be made narrower, more tracks will fit on a disk surface, and more data can be stored on a given disk. The width of the tracks depends on the width of the read/write head used, and in recent years, track widths have decreased as the size of read/write heads have become progressively smaller. This decrease in track width has allowed for dramatic increases in the recording density and data storage of disks.
In a magneto-resistive (MR) sensor changes in the strength and orientation of magnetic fluxes are sensed as changes in electric resistance, as an MR read head encounters changes in magnetic data, as on a computer hard drive. In such an MR sensor, the read head operates based on the anisotropic magneto-resistance (AMR) effect in which the resistance of the read element varies in proportion to the square of the cosine of the angle between the magnetization and the direction of sense current flowing through the sensor. This effect is relatively weak in magnitude, and consequently more attention has been paid in recent years to what is referred to as xe2x80x9cspin valve (SV) effectxe2x80x9d or xe2x80x9cgiant magneto-resistance (GMR) effectxe2x80x9d because of its relatively large magnitude of effect.
In this type of MR sensor, the resistance of a layered magnetic sensor varies due to both spin-depending transfer of conduction electrons between magnetic layers (M1, M2) via a non-magnetic layer (N), and spin-depending scattering at the interfaces between the layers accompanying the transfer of conduction electrons. The in-plane resistance between the pair of ferromagnetic layers (M1, M2), separated by a non-magnetic layer (N), varies in proportion to the cosine of the angle between the magnetization in the two ferromagnetic layers.
In ferromagnetic materials, scattering of electrons depends on the spin on the carriers. Resistivity is proportional to the scattering of electrons. Electrons with A spins parallel to the magnetization direction experience very little scattering and hence provide a low-resistance path. If magnetization of one side of this triple layer (M2) is pinned and M1 is gradually rotated from a parallel to an anti-parallel direction, the resistance of the structure increases in proportion to the cosine of the angle of magnetizations of the two layers M1, and M2. The spin valve is sensitive at low fields because the ferromagnetic layers are uncoupled, therefore a small magnetic field from the magnetic media can rotate the magnetization in one layer relative to the other.
A constant current passes through the sensing region from one electrode terminal (not shown) to another electrode terminal. The total electric resistance of the spin valve changes in proportion to a cosine of an angle between the magnetization direction of the pinned magnetic layer (M2) and the magnetization direction of the free magnetic layer (M1). When the total electric resistance is changed, a voltage difference between the electrode terminals changes and is sensed as read information.
This type of head for writing data is generally configured with two poles separated by a gap layer of non-magnetic material. A typical prior art read/write head is shown in FIG. 4. Layers are generally deposited upon one another and typically include a shield layer 54, a dual gap layer 56, which surround a Magneto-resistive sensor, called MR sensor 58, a pole piece layer, which will be referred to as the bottom pole or P160, a non-magnetic gap layer 62, a first insulation layer or I164, upon which the coils 38 lie, and a second insulation layer, usually referred to as I266, which is generally made from photo-resist material. The top pole 42 is next, and is also commonly referred to as P2. The bottom and top poles 60, 42 each have bottom and top pole tips 72, 74 respectively with pole write gap 76 between them. The Air Bearing Surface ABS 46 and the coating layer 48 are also shown, as well as a back gap 78. The top and bottom poles 42, 60 typically extend from the ABS 46 in a roughly parallel manner until the top pole 42 veers upward to accommodate the thickness of the coils 38 and insulation layers I164 and I266. The bottom pole 60 may also include an extension portion called a pedestal 84.
There are other features which are only apparent from a top or isometric view of the write head. As seen in FIG. 3, the top pole 42 has a main body portion 86 and a narrower portion, commonly referred to as a pole tip or nose 88. The narrow dimension of the top and bottom poles 42, 60 at the write gap 76 determine the track width and also serve to channel the magnetic flux to increase the flux density across the write gap 76. The point at which the nose begins to widen is known as the flare line 90. This is shown in prior art FIGS. 5B, 6B and 8A and B.
The write head is a complex shape in 3 dimensions which cannot be understood by only one view. As seen from the cross-sections 5A and 6A, axes are shown for the x and y directions as the z axis is normal to the plane of the paper in these views. In this view, the top pole P242 has a flat portion covering the main portion of the coils 38, which then begins to curve as the pole approaches the ABS 46 so that the distance between the top pole 42 and the bottom pole P160 narrows. This curved contour portion 92 has a contour boundary 94, at which point the top pole 42 typically includes a flat portion 96 as it approaches the top pole tip 74 (see FIG. 4). FIGS. 5A and B and 6A and B are corresponding cross-sectional and top plan views of two prior art write head architectures. FIGS. 5B and 6B are top plan views similar to FIG. 3 of the top pole P242, and includes axes x and z, the y axis being normal to the plane of the page. As the top pole curved contour 92 curves in the x and y dimensions, the flare 90 widens in the x and z dimensions. FIG. 8A shows an isometric view of the prior art write head 42 with the three axes indicated for reference.
When the flare line 90 of the head lies within the contour boundary 94, then a portion of the pole nose 88 is also curved, or to put it another way, the contour boundary 94 lies closer to the ABS 46 than the flare point 90. Thus the flat portion 96 of the pole nose 88 is small, as seen in FIG. 6B and 8A and B, or practically non-existent as in FIG. 5B.
There are several difficulties in manufacturing write heads such as the ones shown in FIGS. 5A-B, 6A-B and 8A and B. The performance of a write head in many ways is related to how close the flair position can be located to the air bearing surface. The closer it is, the more high performance media that can be written, and the smaller the track width that can be written. The problem in the manufacturing process is to control the structure and the position of the flare. It is much easier to control the fabrication of a structure when it is on a flat surface than it is on a curved surface. This process typically involves photo-lithography, and when light comes down onto a sloped surface, it tends to reflect and scatter out. In contrast, when light comes onto a flat surface, it has a tendency to reflect off the bottom and come back up rather than scattering out. This makes it easier to control the dimensions from a photo-lithography standpoint when the process is performed on a flat surface. Thus, the larger the portion of the pole nose 88 that is flat, the greater control in manufacturing, the better the performance of the head and the greater the ease of manufacture there is.
In addition, in the manufacturing process, air pockets or voids are often inadvertently created thanks to a process known as xe2x80x9cmushroomingxe2x80x9d. As discussed below, these air pockets are a concern when they are formed very close to the air bearing surface ABS, as they can serve as sites for corrosion, and can interfere with the operation of the write head. Thus it is desired that any air pockets which are formed are recessed from the ABS. A write head having the I2 insulation layer close to the ABS would be expected to have air pocket formations closer to the ABS than one which is also recessed from the ABS. If the boundary of the I2 insulation layer is recessed from the ABS, the area of mushrooming will also be recessed, and thus air pockets or voids will necessarily be formed farther from the ABS as well. The write head performance will therefore be improved.
Another concern in fabrication of write heads occurs during the lapping process. The ABS is lapped, which involves removing a small amount of material from the front of the nose. The track width that is written by the head depends on the width of the nose portion at the ABS. The depth, of lapping can vary slightly due to minute variations in processing, and in the fabrication of the top pole. A variation in lapping depth will expose different cross-sections of the nose, so in order to maintain the track width as closely as possible, it is desired that cross-sections will yield the same dimensions as nearly as possible throughout the length of the nose portion or at least the front part of the nose which may be involved in the lapping process. Thus a rectangular cross-section which is uniform in dimension for the length of the nose is much preferred over a cross-section that varies in dimension with the depth of lapping that is performed. A curved upper surface to the nose, of course makes a consistent cross-section difficult to achieve. A flat top surface would thus have advantages in control of track width and ultimately in the track density that can be repeatably achieved during fabrication.
Thus, there is a great need for a write head having a flat top pole, which is thus easier to manufacture and which can be produced with more precise control, and for a method of manufacture which produces this type of write head having a flat top pole.
Accordingly, it is an object of the present invention to produce a write head with a controllable short nose to achieve high recording field for thin top-pole thicknesses, and thus a higher density recording.
Another object of the invention is to produce a write head which has the I2 insulation layer recessed farther from the ABS thus allowing the curvature of sloped portion of the P2 pole to be completed before the start of the flat nose portion. The nose portion is thus more nearly flat allowing for simplified processing steps in its manufacture.
And another object of the invention is to produce a write head in which the photolithography in a broad region around the ABS is be free of topographical reflectionsxe2x80x94thus enhancing the as-plated track width control.
A further object of the present invention is to produce a write head in which photolithography in a broad region around the ABS is free of topographical reflections thus allowing for straight plated side walls of the top-pole structure in the region from the ABS past the flare point (nose). This assures that there is no additional choke point between the designed flare point and the ABS.
An additional object of the present invention is to allow for a mushroomed yoke with mushroom recessed a large distance from the ABS. This implies the cavities under the mushroom will be buried a sufficient margin from the surface to preclude reliability problems associated with cracking and polymer exposure to air.
Yet another object of the present invention is to produce a write head which is uniform or nearly uniform in cross-sectional dimension, so that varying depth of lapping does not substantially affect track width.
Briefly, one preferred embodiment of the present invention is a disk drive write head having in consecutive layers a bottom pole, a write gap layer, a first insulation layer, a coil, a second insulation layer, having an insulation layer boundary, and a top pole on the second insulation layer. The top pole includes a main body portion and a nose portion and has a flare line at the location where the nose portion expands to become the main body portion. The top pole further includes a curved contour portion having a contour boundary, a tip which terminates in an air bearing surface, and a flat portion on the top surface of the nose extending between the tip and the contour boundary. The insulation layer boundary is recessed from the air bearing surface such that the top pole contour boundary lies substantially close to the flare line, thus producing a top pole top surface which is substantially flat.
Also disclosed is a method for fabricating the disk drive write head.
An advantage of the present invention is that critical dimensions are more easily controlled during the fabrication process with a flat nose portion.
Another advantage of the present invention is that the flat surface of the nose portion causes less scattering of light during the photolithography process.
And another advantage of the present invention is that the flare position is several microns from both the ABS and the insulation giving considerable manufacturing margin.
A further advantage of the present invention is that the side walls are substantially straight from flare position to ABS.
A yet further advantage is that due to the essentially consistent width of the write head nose portion, continued lapping of the write head to remove an additional micron of pole tip would not have a significant affect on ABS track width.
Yet another advantage of the present invention is that air pockets formed from mushrooming are formed farther away from the ABS and thus affect reliability of the head to a smaller degree.
These and other objects and advantages of the present invention will become clear to those skilled in the art in view of the description of the best presently known mode of carrying out the invention and the industrial applicability of the preferred embodiment as described herein and as illustrated in the several figures of the drawings.